A conventional approach for ascertaining operational safety of a system is failure analysis of the system. An aspect in determining the operational safety is the determination of the impact on safety resulting from failure of a particular process component, where such analysis can include applying weightings relating to safety, etc. However, certain faults may have a probability of failure that is negligible and, in effect, can be considered in the domain of ‘fault exclusion’, e.g., the fault is excluded from further consideration in determining operational safety. ‘Fault exclusions’ are declared with detailed justification in technical documentation relating to the operational safety of the process. Such operations are determined based upon any of a plurality of operational standards, such as ISO 13849.
However, newer standards are being introduced such that the concept of ‘fault exclusion’ is no longer acceptable when determining operational safety of a process. The newer standards, e.g., EN ISO 13849 Performance Level e (PLe) and EN 62061, can include safety category(ies)/level(s) such as safety integrity level (SIL), which defines a measurement of performance for a safety implemented function. A SIL can be applied to a process indicating most dependable (e.g., an SIL of 4) through to least dependable (e.g., an SIL of 1). For a process to be assigned a higher level of dependability, faults which were previously in the domain of ‘fault exclusion’ have to be defined.
For example, in a conventional system a position of a locking mechanism (e.g., engaged, open, etc.) may have previously been considered under the domain of ‘fault exclusion’, or a series of redundant locking mechanisms may have been provided to render the occurrence of lock failure technically improbable. As such, by utilizing the principle of ‘fault exclusion’, a process may only have a SIL 2 ranking. However, by quantifying one or more operations of the locking mechanism, e.g., (a) is the gate closed?, (b) is the gate locked?, (c) is the locking shaft engaged?, etc., an improved SIL ranking (e.g., a SIL 3 ranking) may be achieved in comparison with the SIL 2 ranking. Furthermore, an extension of attempting to achieve an improved SIL ranking may result in further information being available regarding operation of the locking mechanism, such as an identifier for the locking mechanism, an operational state (e.g., closed, locked, etc.), and the like. Such information, for example, can be utilized in a process utilizing an output signal switching device (OSSD) and in response to an OFF state being generated, for example, a safety-related control system associated with a machine can interrupt a circuit associated with a machine primary control element (MPCE) to place the machine in a safe operating state, as utilized with regard to final switching device (FSD) technologies, for example.
The above-described issues regarding the concept of ‘fault exclusion’ in view of more descriptive standards are merely intended to provide an overview of some of the problems of conventional systems and techniques, and are not intended to be exhaustive. Other problems with conventional systems and techniques, and corresponding benefits of the various non-limiting embodiments described herein may become further apparent upon review of the following description.